This invention relates to a magnetic disc apparatus, and more specifically relates to an apparatus where a magnetic disk (or magnetic discs) and magnetic heads are contained in a sealed up space made between a base plate and its cover.
FIG. 5 shows an example of a cross sectional view of such magnetic disc apparatus of prior art. The apparatus shown by FIG. 5 comprises a magnetic disk 1 rotated by a spindle motor 2, a magnetic head 3 which magnetically couples to the magnetic disc 1, a carriage 4 which displaces the magnetic head 3 in a radial direction of the magnetic disk 1, a base plate 5 on which the carriage 4 is mounted, and a cover 6 for making a sealed up space between the base plate 5 for containing the magnetic disk 1 with the spindle motor 2 and the magnetic head 3 with the carriage 4.
A housing 11 of the spindle motor 2 is fixed to the base plate 5, and in a central portion of the housing 11, a ball bearing having an upper ball bearing 12 and a lower ball bearing 13, is fixed. A spindle 14 of the spindle motor 2 is supported rotation-free by the ball bearing. On top of the spindle 14, a cylindrical hub 15 having a hollow inner space is fixed at the axial center.
The magnetic disc 1 is mounted on the perimeter of the hub 15, clamped by a clamper 16, and is rotated by the spindle 14. The spindle motor 2 comprises a stator unit 18 and a rotor unit. The rotor unit is fixed to the hub 14 with its pole pieces 17 of permanent magnet and a yoke 19 which makes magnetic circuits between the pole pieces. The stator unit 18 comprising stator windings and stator magnetic circuits, is fixed to the housing 11, surrounding the outer ring of the ball bearing. Thus, central axis of the rotor unit is aligned to that of the stator unit 18, and an adequate clearance is maintained between the faces of the pole pieces 17 and the circumference of the stator unit 18.
When the stator windings are excited, the rotor unit of the spindle motor 2 rotates the hub 15 and the magnetic disk 1 clamped to the hub 15.
In a heretofore known magnetic disc apparatus as shown in FIG. 5, all the component parts of the spindle motor 2 together with the housing 11 and the bearing of the spindle are fixed on the base plate 5, and spaces near the cover 6 are not effectively utilized.